A 16-year-old East Palo Alto boy charged with attempted murder for an October drive-by shooting that injured three people pleaded not guilty this week, according to the San Mateo County District Attorney’s Office.

Rodolfo Medina-Barragan, a Norteno gang member, will be tried as an adult, Assistant District Attorney Al Serrato said Thursday.

“Murder and attempted murder, particularly in a gang, is one of the most serious threats to social order,” Serrato said. “Sixteen is young, but it’s not a 12-year-old, and with the level of violence and potential for harm …we’re moving well past what the juvenile system was meant to deal with.”

According to prosecutors, Barragan and others drove down Myrtle Street in Menlo Park on Oct. 29 and sprayed gunfire at a house, hitting three people. Three firearms were used in the attack, based on the recovered casings.

During a probation search that month, Medina-Barragan was found with a .40 caliber handgun that matched casings found in the street. Prosecutors say he also was at the wheel of the Toyota Corolla used in the drive-by; the car eventually was found and tied to a relative, Erick Barragan.

Medina-Barragan is charged with three counts of attempted murder and three counts of shooting into an inhabited building. The charges also have special circumstances because of his alleged gang involvement and use of a gun. If convicted and given consecutive sentences, he faces 45 years to life in prison, Serrato said.

There is an arrest warrant outstanding for Barragan, who faces similar charges, Serrato added.

Although Medina-Barragan was arrested shortly after the October shooting, he was later released because there was not sufficient evidence to prosecute him, District Attorney Steve Wagstaffe told The Daily News earlier this month.

“The police detectives continued to work the case and eventually came up with sufficient evidence to support going forward with a prosecution,” Wagstaffe wrote in an email. His office filed charges in June and issued a warrant for Medina-Barragan’s arrest, according to Wagstaffe.

Medina-Barragan is being held without bail. His defense attorney, Gerritt Rutgers, could not be reached for comment Thursday.